Automatic sprinklers have come a long way since Henry
H. Parmalee introduced the first practical automatic sprinkler in 1874.1
Parmalee's sprinkler led to a major step in the advancement of
industrial fire protection. Prior to the introduction of his sprinkler,
sprinkler systems typically consisted of steel pipes equipped with
perforated holes through which water would flow, similar to today's
deluge-type sprinkler system. Roughly seven years after the introduction
of the Parmalee sprinkler, Frederick Grinnell began modifications to
the sprinkler that allowed for it to be more effective and produced at a
lower cost.

With the advent of the automatic
sprinkler system came guidelines for sprinkler system installations as
well as guidelines for sprinkler system designs. On November 16, 1891,
the Associated Factory Mutual Insurance Company (now known as FM Global)
released the first automatic sprinkler system installation guideline
entitled, Location and Spacing for Automatic Sprinklers. The
design for automatic sprinkler systems became rooted on a pipe schedule
basis where the size of the sprinkler system piping was based on the
number of sprinklers located downstream of the pipe. The pipe schedule
method was divided into three categories: light hazard, ordinary hazard
and extra hazard pipe schedule. Based on the anticipated hazard of the
occupancy to be protected, the size of the sprinkler system pipe was
then determined by the number of sprinklers that were installed
downstream of it.

The pipe schedule design method offered a simple means for
determining the proper size of a sprinkler system. It, however, did not
take into account the water supply available for the automatic sprinkler
system, nor did it allow for flexibility when the occupancy hazard
protected by an existing sprinkler system increased. Even with these
drawbacks to the pipe schedule design method, automatic sprinkler
systems prior to the 1950s did an excellent job of keeping fires under
control until the local fire service was able to arrive and manually
extinguish the blaze. This was due in large part to the combustible
loading of the stored materials being relatively low, coupled with the
relatively low storage and ceiling heights maintained in warehouse
areas.

However, at the start of the 1950s,
changes in industrial practices demonstrated the limitations of the pipe
schedule design method. At this time came (1) an increased use of steel
supported building structures, (2) the invention of the fork-lift truck
and (3) an increased use of plastic materials.

Although the use of steel allowed
buildings to be built higher than before, steel weakens at elevated
temperatures. Since industrial fires can exceed these elevated
temperatures, they create a condition where a building structure could
possibly collapse due to the failure of a steel column even when
automatic sprinkler protection was provided at ceiling level.

The invention of the fork-lift truck
allowed storage height to be dramatically increased, which prior to the
1950s was only about 6 to 8 ft (2.0 to 2.4 m) high, or as high as a
person could lift the stored item. In addition, most commodities
maintained in storage areas prior to this timeframe consisted of
ordinary combustibles, such as materials made from metal, glass or wood.
The introduction of plastic materials increased the fire hazard within
industrial facilities as the heat of combustion is two to three times
higher than ordinary combustibles.2

To account for these changes, research conducted at FM Global in the 1950s3
led to two major changes in fire protection. The first major change was
the introduction of the standard spray automatic sprinkler, which
modified the sprinkler deflector to discharge nearly all of the water
towards floor level in a parabolic shape. The second major change was
the introduction of the density/area design concept. This concept
identified a specific flow rate per sprinkler for all sprinklers
operating within an indicated area. Unlike the pipe schedule design
method, the density/area design concept required the water supply to be
evaluated to verify that it could provide the necessary flow and
pressure for the required design.

Although the design/area design concept
worked well, testing at FM Global in the 1960s and 1970s demonstrated
that the sprinkler technology at that time was not very effective for
storage-type occupancies. As a result, research was initiated at FM
Global in the 1970s to develop a sprinkler specifically intended for the
protection of storage. This research led to the development of the
"large-drop" sprinkler. This advancement in sprinkler performance also
led to a new design format, one based on a specified minimum operating
pressure at the most remote sprinkler while simultaneously opening an
indicated number of sprinklers. A decade later, FM Global used the
knowledge gained from the large-drop sprinkler program, coupled with
another project from the 1970s that helped develop the quick-response
thermal element, to develop the sprinkler concept that would eventually
lead to the development of the "early suppression fast response"
sprinkler, or ESFR for short. The design format for the ESFR sprinkler
was also based on the same design format used with the large-drop
sprinkler.

By the start of the 21stcentury,
sprinklers were commercially available in various K-factor sizes,
orientations, nominal temperature ratings, RTI ratings, finishes and
spacing coverage. They had been grouped into three categories, known
today by the terms "control mode density area" (CMDA), "control mode
specific application" (CMSA) and "suppression mode" (formerly called
ESFR) sprinklers. The first two categories group sprinklers by an
assumed performance during a fire event (i.e., control of a fire) where
as suppression mode sprinklers are assumed to suppress any fire that
they protect. The assumed suppression performance allows for a reduced
number of sprinklers in the design area (typically 12 sprinklers) as
well as a reduced hose stream allowance (250 gpm [950 Lpm]) and
sprinkler system duration (1 hour). The CMDA sprinklers differ in design
format as they utilize the density/area design format whereas both the
CMSA and suppression mode sprinklers use the number of sprinklers at a
given minimum pressure design format.

Automatic sprinkler protection is the
best line of defense against fire within an industrial facility;
however, since the release of the first installation and design
guidelines back in 1891, the requirements for automatic sprinklers have
become much more complex. Prior to 2010, FM Global's installation
guidelines for automatic sprinklers were provided in the following three
data sheets: Data Sheet 2-2, Installation Rules for Suppression Mode Automatic Sprinklers,4 Data Sheet 2-7, Installation Rules for Sprinkler Systems Using Control Mode Specific Application (CMSA) Ceiling Sprinklers for Storage Applications,5 and Data Sheet 2-8N, NFPA 13 Standard for the Installation of Sprinkler Systems, 1996 Edition,6
encompassing a total of 344 pages. In addition, the design guidelines
for typical warehouse occupancies, covered in FM Global Data Sheet 8-9, Storage of Class 1, 2, 3, 4 and Plastic Commodities,7 consisted of 123 pages.

To help reduce the complexity of
automatic sprinkler installation and design, FM Global established a new
method of classifying automatic sprinklers in 2010. Instead of
categorizing sprinklers based on an assumed performance during a fire
event, such as control mode or suppression mode sprinklers, FM Global
now categorizes sprinklers based on intended application using the terms
"storage sprinklers," "non-storage sprinklers" and "special protection
sprinklers." The intended application of storage sprinklers is for
protection of storage-type occupancies as well as other high heat
release occupancies. The intended application of non-storage sprinklers
is for the protection of non-storage occupancies, such as offices as
well as manufacturing or other moderate heat release rate occupancies.

The intended application of special protection sprinklers is for the
protection of occupancies not generally covered by the other two
categories.

This new method allows for a clearer understanding of the
compatibility of the sprinklers with the occupancy they are to protect
and allows for a single design format for all sprinklers. FM Global has
chosen the number of sprinklers at a given minimum pressure design
format to allow the design of a sprinkler system to be based on the
actual performance of the chosen sprinkler as opposed to an assumed
performance or, in the case of the density/area design method, the
performance of the least efficient sprinkler.

Based on this new approach, FM Global has
taken its three data sheets for sprinkler system installation and
combined them into a single document entitled Data Sheet 2-0, Installation Guidelines for Automatic Sprinklers.8
The installation guidance provided within this new document addresses
the specific requirements for storage sprinklers, non-storage sprinklers
or special protection sprinklers, coupled with the installation
guidelines that are common to all three types of sprinklers.

Also, as a result of this new approach,
FM Global Data Sheet 8-9 now references the use of FM Approved storage
sprinklers at ceiling level and when needed, as in-rack sprinklers. In
addition, the ceiling-level designs offered in Data Sheet 8-9 are now
based on five attributes associated with a sprinkler: (1) K-factor, (2)
orientation, (3) response time index (RTI) Rating, (4) sprinkler spacing
and (5) temperature rating.

*Based
on maximum water delivery time of 25 seconds **Based on maximum water
delivery time of 20 seconds ***The protection options indicated in the
protection table can be based on any ceiling height equal to or higher
than the actual maximum ceiling height of the protected area. ****The
protection options indicated in the protection table for upright
sprinklers can also be used as an alternative option for pendent
sprinklers having the same K-factor, RTI rating, nominal temperature
rating and spacing requirements as the upright sprinkler. *****The
design of 8 @ 40 (2.8) has a hose stream allowance of 250 gpm (950L/min)
and a duration of 60 minutes when the maximum linear spacing is up to
12 ft (3.6 m); for linear spacing over 12 ft (3.6 m) the hose stream
allowance is 500 gpm (1,900 L/min) and the duration is 120 minutes.

By going to the storage sprinkler
concept, the design approach for sprinklers within Data Sheet 8-9 is now
based on the number of sprinklers operating at a given minimum
pressure. This means that the design approach of density/area has been
eliminated from Data Sheet 8-9. To many in the fire protection
community, this may appear illogical as sprinkler systems that have been
installed using the density/area design format have performed very well
since the design concept was introduced in the 1960s. However, FM
Global feels there are limitations with this design approach. These
limitations include: (1) current density/area protection tables must be
based on the performance of the least effective sprinkler listed for the
table, and (2) the ability of the most remote sprinkler's design
pressure must be dependent on the installed sprinkler's spacing.

For the first point, consider two full-scale fire tests conducted at FM Global's Research Campus.9
The tests involved open-frame rack storage of cartoned expanded
plastics to 15 ft (4.5 m) high under a 30 ft (9.1 m) high ceiling with
an 8 ft (2.4 m) wide aisle provided between storage racks. The tests
used CMDA standard-response K11.2 (K160) 160°F (70°C) nominally rated
sprinklers on 10 x 10 ft (3.0 x 3.0 m) spacing. For the first test, this
arrangement was protected using a 1.00 gpm/ft2 (40 mm/min) density with an upright sprinkler, whereas the second test was conducted using a 0.60 gpm/ft2 (24 mm/min) density with a pendent sprinkler. With the 1.00 gpm/ft2 (40 mm/min) density and an upright sprinkler, the test resulted in 32 sprinklers opening,3 whereas only 10 sprinklers opened using the 0.60 gpm/ft2 (24 mm/min) density with a pendent sprinkler.4
These two tests help to demonstrate that density is not a driving
factor for sprinkler system design. In addition, using today's
density/area design concept, the design for both sprinklers would be the
same and would have to be based on the results of the K11.2 (K160)
upright sprinkler, which had the poorer performance in this particular
test.

The test comparison outlined above is representative of many of the
tests that FM Global has conducted over the decades when comparing
various sprinkler attributes. In general, test results will differ when a
sprinkler's K-factor, orientation, RTI rating and nominal temperature
rating is changed. What tests over the past 40 years have demonstrated
is that the amount of water that is discharged from ceiling-level
sprinklers in terms of an applied density is not as important as the
amount of water that actually reaches the fire area, which can be
thought of as an actual delivered density (ADD). What helps increase the
ADD during a fire event can be found in the aforementioned attributes
of a sprinkler, namely orientation, K-factor, RTI rating, temperature
rating and, in some degree, sprinkler spacing. Because of this, FM
Global now uses these five attributes to define the protection required
for storage arrangements handled by Data Sheet 8-9 using the number of
sprinklers at a given minimum pressure design format. A protection table
from Data Sheet 8-9 is shown in Figure 1.

In addition to being easy to read, this
protection table actually replaces a total of 9 protection tables from
the June 2009 version of Data Sheet 8-9, making it less complicated than
prior versions.

By moving to the new categorization of Storage sprinklers,
FM Global has created a new method by which the hose stream allowance
and the duration of a sprinkler system is determined. FM Global now
bases the hose stream allowance and the required duration of a sprinkler
system, in general, on the number of sprinklers in the ceiling design
chosen. Some of the protection options shown in Figure 1 are highlighted
with a green background. What these highlighted options represent are
options that require only a 250 gpm (950 Lpm) hose stream allowance and a
duration of only 1 hour.

With these changes, coupled with anticipated future
changes in both FM Global Data Sheets 2-0, 8-9 and other design-based
data sheets, FM Global aims to provide the most effective installation
and design protection options, which are intended to be simpler to
understand, less costly to install, but a more sustainable choice.

About SFPE

SFPE is a global organization representing those practicing in the fields of fire protection engineering and fire safety engineering. SFPE’s mission is to define, develop, and advance the use of engineering best practices; expand the scientific and technical knowledge base; and educate the global fire safety community, in order to reduce fire risk. SFPE members include fire protection engineers, fire safety engineers, fire engineers, and allied professionals, all of whom are working towards the common goal of engineering a fire safe world.